Carla Giordani Testa

Induction of oxidative stress in rat brain by the metabolites accumulating in maple syrup urine disease

Maple syrup urine disease (MSUD) is an inherited disorder caused by deficiency of branched‐chain l‐2‐keto acid dehydrogenase complex activity. Affected patients present severe brain dysfunction manifested as convulsions, coma, psychomotor delay and mental retardation. However, the underlying mechanisms of these neurological findings are virtually unknown. In this study, we tested the in vitro effect of l‐leucine, l‐isoleucine and l‐valine, the amino acids accumulating in MSUD, on the lipid peroxidation parameters chemiluminescence and thiobarbituric acid‐reactive substances (TBA‐RS), as well as on total radical‐trapping antioxidant potential (TRAP) and total antioxidant reactivity (TAR) in cerebral cortex from 30‐day‐old rats. l‐Leucine significantly increased chemiluminescence and TBA‐RS measurements and markedly decreased TRAP and TAR values. l‐Isoleucine increased chemiluminescence and decreased TRAP measurements, but TAR and TBA‐RS levels were not altered by the amino acid. Finally, TRAP measurement was diminished by l‐valine. The results indicate a stimulation of lipid peroxidation and a reduction of brain capacity to efficiently modulate the damage associated with an increased production of free radicals by the branched‐chain amino acids (BCAAs) accumulated in MSUD. It is therefore tempting to speculate that oxidative stress may be implicated in the brain damage found in MSUD patients.

Glutaric acid induces oxidative stress in brain of young rats.

This study investigated the effects of glutaric acid, which predominantly accumulates in glutaric acidemia type I, on some in vitro parameters of oxidative stress in brain of young rats. We evaluated chemiluminescence, total radical-antioxidant potential (TRAP) and the activities of the antioxidant enzymes catalase, glutathione peroxidase and superoxide dismutase in brain tissue homogenates in the presence of glutaric acid at concentrations ranging from 0.05 to 2.0 mM. The acid significantly increased chemiluminescence (up to 65%) and reduced total radical-antioxidant potential (up to 28%) and glutathione peroxidase activity (up to 46%), without affecting catalase and superoxide dismutase activities. The results provide evidence that glutaric acid induces oxidative stress in vitro in rat brain. If these findings also occur in humans, it is possible that they may contribute to the neuropathology of patients affected by glutaric acidemia type I.

γ-Hydroxybutyric acid induces oxidative stress in cerebral cortex of young rats

GHB is a naturally occurring compound in the central nervous system (CNS) whose tissue concentration are highly increased during drug abuse and in the inherited deficiency of succinic semialdehyde dehydrogenase (SSADH) activity. SSADH deficiency is a neurometabolic-inherited disorder of the degradation pathway of gamma-aminobutyric acid (GABA). It is biochemically characterized by increased concentrations of gamma-hydroxybutyric acid (GHB) in tissues, cerebrospinal fluid (CSF), blood and urine of affected patients. Clinical manifestations are variable, ranging from mild retardation of mental, motor, and language development to more severe neurological symptoms, such as hypotonia, ataxia and seizures, whose underlying mechanisms are practically unknown. In the present study, the in vitro and in vivo effects of GHB was investigated on some parameters of oxidative stress, such as chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR), as well as the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in homogenates from cerebral cortex of 15-day-old Wistar rats. In vitro, GHB significantly increased chemiluminescence and TBA-RS levels, while TRAP and TAR measurements were markedly diminished. In contrast, the activities of the antioxidant enzymes SOD, CAT and GPX were not altered by GHB in vitro. Acute administration of GHB provoked a significant enhance of TBA-RS levels and a decrease of TRAP and TAR measurements. These results indicate that GHB induces oxidative stress by stimulating lipid peroxidation and decreasing the non-enzymatic antioxidant defenses in cerebral cortex of young rats. If these effects also occur in humans, it is possible that they might contribute to the brain damage found in SSADH-deficient patients and possibly in individuals who consume GHB or its prodrug gamma-butyrolactone.

Effects of histidine and imidazolelactic acid on various parameters of the oxidative stress in cerebral cortex of young rats.

Histidinemia is an inherited metabolic disorder caused by deficiency of histidase activity, which leads to tissue accumulation of histidine and its derivatives. Affected patients usually present with speech delay and mental retardation, although asymptomatic patients have been reported. Considering that the pathophysiology of the neurological dysfunction of histidinemia is not yet understood and since histidine has been considered a pro‐oxidant agent, in the present study we investigated the effect of histidine and one of its derivatives, l‐β‐imidazolelactic acid, at concentrations ranging from 0.1 to 10 mM, on various parameters of oxidative stress in cerebral cortex of 30‐day‐old Wistar rats. Chemiluminescence, total radical‐trapping antioxidant potential (TRAP), thiobarbituric acid reactive substances (TBA‐RS), and the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH‐Px) were measured in tissue homogenates in the presence of l‐histidine or l‐β‐imidazolelactic acid. We observed that l‐histidine provoked an increase of chemiluminescence and a reduction of TRAP at concentrations of 2.5 mM and higher, while TBA‐RS measurement, GSH‐Px, CAT and SOD activities were not affected. Furthermore, l‐β‐imidazolelactic acid provoked antioxidant effects at high concentrations (5–10 mM) as observed by the reduction of chemiluminescence, although this compound enhanced chemiluminescence at low concentrations (0.5–1 mM). These results suggest that in vitro oxidative stress is elicited by histidine but only at supraphysiological concentrations.